Bisque Firing vs Glaze Firing: What Each One Does

Most beginners are surprised to learn that a finished ceramic piece typically goes through the kiln twice. Understanding bisque firing vs glaze firing clears up a lot of confusion about the pottery process and helps you plan your work much more confidently. Each firing has a specific job, and skipping or rushing either one usually shows up as a cracked, crawled, or undercooked piece.

Why Pottery Is Usually Fired Twice

The short answer: clay and glaze have different needs, and trying to satisfy both in one firing is genuinely difficult.

Raw clay, called greenware, still contains chemically bonded water locked inside the clay particles themselves. This is different from surface moisture you can feel. Even clay that seems bone dry has this water, and if you heat it too fast, steam pressure builds and the piece can crack or explode. The bisque firing drives out that water slowly and burns off organic matter in the clay. What comes out is a hard, porous, bone-white (or terracotta-colored) piece called bisqueware.

Bisqueware is tough enough to handle without denting, but still porous enough to absorb glaze evenly. That porosity is the whole point. Pour liquid glaze over greenware and it slumps or absorbs unevenly. Pour it over an already vitrified, glassy surface and it beads off. Bisqueware is the sweet spot.

The glaze firing then melts the powdered minerals in the glaze into a smooth, glassy coating and brings the clay body to its final hardness. Depending on your clay and glaze, this second firing may reach significantly higher temperatures than the first.

If you're newer to how kilns actually generate and distribute that heat, this beginner's guide to how a pottery kiln works covers the mechanics well.

What Is Bisque Firing?

Bisque firing is the first firing, transforming fragile greenware into bisqueware. The greenware to bisque transformation is not optional for most production potters. It's the step that makes everything downstream easier.

Typical Temperatures for Bisque

Most studio potters bisque fire to cone 06 or cone 04. In Fahrenheit, cone 06 is around 1828°F (998°C) and cone 04 is around 1945°F (1063°C). These are lower than most final clay maturing temperatures, which is intentional. You want the piece sintered and sturdy, but not fully vitrified.

What Happens Inside the Kiln During Bisque

The firing schedule matters a lot here, especially at the start. During the early stages (roughly up to 212°F / 100°C), any remaining surface moisture burns off. Then, between about 842°F and 1112°F (450°C to 600°C), chemically bonded water releases from the clay structure. This is the phase where impatient ramp speeds cause explosions. Most potters hold (soak) at around 250°F (121°C) for a period to be safe, then ramp slowly through the quartz inversion point at 1063°F (573°C), where silica crystals shift structure.

Organic material in the clay, including any paper clay additives or plant matter, also burns away during bisque. By the end, the clay is chemically changed. It's no longer raw clay that will turn back to mud if it gets wet. But it's not glass yet either.

What Bisqueware Looks and Feels Like

Pull a piece from the bisque and you'll notice it feels almost chalky. It's surprisingly lightweight. The color often turns a pale cream or terracotta depending on your clay body. It has no shine at all. If you tap it, it makes a clear ringing sound, which is actually a useful test. A dull thud can mean the piece has cracks or wasn't fully sintered.

What Is Glaze Firing?

The glaze firing is the second and final trip through the kiln. This is where the glaze melts, bubbles, and resolves into the surface you intended. The clay body also matures fully during this firing.

Typical Temperatures for Glaze Firing

Glaze firing temperatures depend entirely on your clay body and glazes. Earthenware clays and their glazes typically mature around cone 06 to cone 02 (1828°F to 2048°F / 998°C to 1120°C). Mid-fire stoneware is common at cone 5 or cone 6 (2167°F to 2232°F / 1186°C to 1222°C). High-fire stoneware and porcelain go to cone 9 or cone 10 (2300°F to 2345°F / 1260°C to 1285°C).

Mixing up clay and glaze temperatures is one of the most common beginner mistakes. A low-fire glaze on a high-fire clay body will look dull and underfired. A high-fire glaze on low-fire clay can cause the clay to bloat or collapse.

What Happens to the Glaze in the Kiln

As temperatures rise, the raw powdered minerals in your glaze start to melt. There's an ugly phase around 1800°F to 2000°F where most glazes look rough and bubbly. Don't open the kiln to check. By peak temperature, the glaze is fully fluid, and during the slow cooling, it solidifies into glass bonded to the clay surface.

The clay body simultaneously vitrifies during glaze firing. Silica and alumina particles sinter together more completely, filling in pores. Most stoneware becomes dense and water-resistant. Earthenware remains more porous even after glaze firing, which is why unglazed earthenware absorbs water.

The Cooling Phase

Glaze firing cooling is not passive. Slow cooling through the quartz inversion (1063°F / 573°C) matters again on the way down. Crash cooling through this range can cause dunting, which are invisible internal cracks that sometimes cause pieces to shatter later. Electric kilns hold heat better than wood or gas kilns, which helps, but leaving the kiln closed until it reaches at least 200°F (93°C) before cracking the lid is a good habit.

Bisque Firing vs Glaze Firing: Side by Side

Feature	Bisque Firing	Glaze Firing
Purpose	Sinter greenware, drive out moisture and organics	Melt glaze, mature clay body fully
Typical cone	Cone 06 to cone 04	Cone 06 (earthenware) to cone 10 (high-fire)
Approximate temp	1828°F to 1945°F (998°C to 1063°C)	1828°F to 2345°F (998°C to 1285°C)
What goes in	Bone-dry greenware	Glazed bisqueware
What comes out	Porous, matte bisqueware	Finished, (usually) glassy ceramic
Glaze applied?	No	Yes
Reversible?	No (clay is changed chemically)	No

Key differences at a glance:

• Bisque firing removes water and organic material; glaze firing melts minerals into glass.
• Bisqueware is porous and matte; finished glazed ware is dense and often shiny.
• Bisque temperatures are usually lower than glaze temperatures (for mid and high-fire work).
• The pot is fragile before bisque, handleable after bisque, and permanent after glaze firing.
• Glaze will not adhere properly to greenware or to over-vitrified bisqueware.

Do You Always Need Two Firings?

Not always. Single firing (also called once-firing or raw glazing) skips the bisque step entirely. Glaze is applied to leather-hard or bone-dry greenware and the whole thing goes straight to the glaze firing. This saves time, fuel, and kiln space. Some potters who work primarily with slips and traditional techniques use this method.

The risk is higher. Greenware is fragile and easily damaged during glazing. The glaze and clay body need to shrink at compatible rates through the entire firing range, which is harder to calibrate. Crawling and cracking are more common. For beginners, the two-firing method gives you more control and more opportunities to catch problems early.

Also worth knowing: some potters glaze a piece and fire it a third time to add overglaze enamels, gold lusters, or china paints. Those decorative firings run much lower, often around cone 018 to cone 015.

If you're still sorting out drying and don't have kiln access yet, what to do if you don't have a kiln covers your options before you commit to a firing schedule.

Getting Your Greenware Ready for Bisque

The most important thing you can do before bisque firing is make sure the piece is genuinely bone dry. This sounds obvious but takes longer than most beginners expect. A pot that feels dry to the touch can still hold moisture in thicker walls or at the base. Check with the back of your hand for any coolness. Slow dryers and pieces with thick bottoms may need a week or more in a dry environment.

Proper drying before firing is where a lot of kiln disasters start. How to dry pottery before firing so it doesn't crack goes into the details on this step.

Loading bisque kilns is fairly forgiving. Pieces can touch each other (not stacked with weight on them, but rims touching is fine). Lids should be fired on their pieces to prevent warping from matching shrinkage. Shelves need kiln wash to prevent drips from earlier glaze residue sticking pieces down.

Glaze kiln loading is stricter. Glazed pieces cannot touch each other or the kiln shelf. Leave at least a quarter inch of space between pieces. The foot (bottom ring) should be wiped free of glaze before firing to prevent the pot from permanently fusing to the shelf.

Frequently Asked Questions

Can I skip the bisque firing and glaze greenware directly?

You can, but it takes experience and the right combination of clay and glaze. Raw glazing works best with certain stoneware bodies and slip glazes that have been tested for single firing. For most beginners, the two-firing approach is more reliable because you can inspect the bisqueware for cracks before investing in glazing.

What cone should I bisque fire to?

Most studio potters use cone 06 or cone 04 for bisque firing regardless of their clay's final maturing temperature. A cone 06 bisque is appropriate for earthenware, mid-fire, and high-fire clays alike. The bisque just needs to be hard enough to handle and porous enough to absorb glaze.

Why did my glaze crawl or peel off?

Crawling usually happens because the glaze pulled away from the clay surface during firing. Common causes include applying glaze too thick, firing bisqueware that was dusty or had oil from your hands on it, or under-firing the bisque so it remained too weak to hold the glaze. Wipe bisqueware with a clean damp sponge before glazing if it's been sitting around.

Does the bisque firing temperature affect the glaze?

Yes. If you bisque fire too high, the clay becomes less porous and won't absorb glaze well. If you bisque too low, the clay may not be sintered enough, which can cause issues in the glaze firing. Staying in the cone 06 to cone 04 range keeps the bisqueware in the right porosity window for most commercial and studio glazes.

Can I re-fire a piece that came out wrong from the glaze kiln?

Sometimes. If a glaze color came out dull or the coverage was uneven, you can apply additional glaze over the fired surface and re-fire. Glaze doesn't stick as well to a vitrified surface as it does to bisqueware, so apply it thinner and be prepared for some crawling. Chipped, cracked, or collapsed pieces generally cannot be rescued by re-firing.